To assure safety in air travel, for example, it is necessary to check luggage for items, particularly explosive agents or materials, by employing the most modern technical equipment. In the process, an object (luggage) typically passes through one or more stages (levels). The first level usually comprises a fast X-ray system designed to handle the large number of luggage items to be tested. If a piece of luggage contains materials that cannot be clearly identified, an additional test is performed in a second level.
As disclosed in German Patent DE 44 06 956 C2, for an accelerated check in the second, or higher, stage, a plurality of coordinates of the regions that were not unambiguously determined in the lower, first stage is detected distinctly by a computer and transmitted to the second or higher stage.
The method of X-ray diffraction can be employed, particularly in the search for explosive materials. In this method, X-ray radiation that has been scattered by the crystal structure of an item is measured and compared to the characteristic energy spectra of, for example, various explosive materials. These spectra give an indication of the presence of an explosive material and additionally information about the explosive material in the object.
German published patent application DE 195 10 168 A1 discloses an apparatus designed for this purpose. In this case, a fanned X-ray beam is generated at the X-ray source by means of a collimator or aperture, and is then radiated onto a test region of a material to be tested. Slot-shaped collimators are disposed symmetrically around the axis of the central X-ray beam, specifically in a plane that extends perpendicular to the fan plane of the X-ray, on the side of the test region opposite the X-ray source. A plurality of detectors performs the evaluation over the entire X-rayed test region.
European published patent application EP 0 354 045 A2 also discloses an apparatus and a method in which a fanned X-ray beam is generated. This fanned beam radiates through the object to be tested, and is diffracted at the lattice structure of the object, with the diffraction being recorded as an energy spectrum by a plurality of detectors. U.S. Pat. No. 4,956,856 discloses a further apparatus. In this case, a narrow X-ray beam(pencil beam) is generated and directed, by means of a rotating roller having a spiral-shaped slot, at an object to be X-rayed. The pencil beam passes through the slot transversely to the object to be tested.
German published patent application DE 41 01 544 A1 discloses the use of a primary beam having a small cross section in an X-ray device. Here, a plurality of detectors and a concentric collimator arrangement detects the scatter radiation generated from the primary beam.
A drawback of the aforementioned apparatuses is that the entire piece of luggage must always be sampled or scanned in order to ascertain all unacceptable luggage items.
An arrangement for generating an expanded X-ray bundle is known from German published patent application DE 41 30 039 A1. A collimator arrangement used for this purpose comprises two limiting bodies, which are oriented relative to one another such that they limit a space corresponding to the shape of the ray bundle. This arrangement serves to increase the surface impacted by the X-ray.